seltzer vs mineral water

seltzer and mineral water both are nouns.

Word	Noun	Adjective	Verb	Adverb
seltzer	Yes	No	No	No
mineral water	Yes	No	No	No

As nouns, mineral water is a hypernym of seltzer; that is, mineral water is a word with a broader meaning than seltzer:

seltzer: naturally effervescent mineral water
mineral water: water naturally or artificially impregnated with mineral salts or gasses; often effervescent; often used therapeutically

seltzer (noun)	mineral water (noun)
naturally effervescent mineral water	water naturally or artificially impregnated with mineral salts or gasses; often effervescent; often used therapeutically
effervescent beverage artificially charged with carbon dioxide